This invention relates to a process for the preparation of silylisocyanates.
Various methods for the preparation of silylisocyanates are known (see, e.g., Houben Weyl, 13/5, page 126 et seq (1979)). According to German Offenlegungsschrift No. 1,965,741, silylisocyanates may be prepared by reacting silylhalides with salts of cyanic acid. Methods employing urea instead of cyanic acid salts have been investigated by J. Goubeau and D. Paulin (see Ber. 93, 111 (1960)). Since urea is not split to give off isocyanic acid until it reaches a temperature of about 130.degree. C. and silylchlorides are already gaseous at this temperature at atmospheric pressure, Goubeau and Paulin were forced to carry out the synthesis reaction under pressure. They found that the reaction of trimethyl silylchloride with urea started at 240.degree. C. and that a maximum yield of trimethyl silylisocyanate (amounting to 65-75% of the theoretical yield) was obtained within 4 to 5 hours if the reaction was carried out at 300.degree..+-.20.degree. C. However, reaction of dimethyl silyldichloride with urea yielded at most 5-10% of the theoretical yield of dimethyl silyldiisocyanate and substantial quantities of [(CH.sub.3).sub.2 SiO].sub.3 and [(CH.sub.3).sub.2 SiO].sub.4 as well as biuret, ammonium cyanate, cyanuric acid and tricyanile urea as by-products. A considerable proportion of the starting compounds therefore reacted to form by-products which could not be recycled.